Hydraulic control for die pads in presses



March 10, 1964 F. M. WILLIAMSON 3,124,340

HYDRAULIC CONTROL FOR DIE PADS IN PRESSES Filed June 1, 1961 2 Sheets-Sheet 1 E31 W W March 10, 1964 F. M. WILLIAMSON 3,124,340

HYDRAULIC CONTROL FOR DIE PADS IN PRESSES Filed June 1, 1961 2 Sheets-Sheet 2 INVENTORQ United States Patent 3,124,340 HYDRAULIC CONTRDL FOR DIE PADS IN PRESSES Floyd M. Williamson, Di-Dro Engineering Co., 2405 E. Grand Blvd, Detroit, Mich. Filed June 1, 1961, Ser. No. 114,264 6 Claims. ((11. 2671) This invention relates to a hydraulic control system for a movable die pad in a press wherein the movable die pad is provided with a hydraulic cushion which provides a predetermined degree of resistance to movement of the die pad to its retracted position upon closing of the press and moves the die pad to its extended position upon opening of the press. A system of this type generally comprises a piston reacting against the die pad and movable within a cylinder which is connected to a source of hydraulic fluid under relatively low pressure and a pressure relief valve through which the fluid is returned from the cylinder to the pressure fluid source upon closing of the press. The pressure in the supply tank is effective to return the die pad to its extended position when the press opens. If the die pad is to perform a stripping operation upon opening of the press, the pressure in the supply tank may not be large enough to provide the necessary stripping action unless the size of the piston is increased beyond that necessary for the proper operation of the die pad and cushion on the Working stroke of the press. An increase in the size of the piston requires a larger size pressure relief valve which is undesirable not only from the standpoint of economy but also because of the increased velocity of fluid flow which results in high heat generation in the system, particularly in high speed press operations.

A booster cylinder may be employed to assist in the stripping operation with a larger diameter piston supplied with air under the low pressure to cause a smaller diameter piston to force fluid at high pressure to the hydraulic cushion cylinder. Such arrangements may be satisfactory at lower speed operations, but at higher speeds the booster piston cannot be actuated rapidly enough and its momentum prevents uniform movement of the booster piston and the press may even complete its cycle of operation before the booster piston is effective to supply the high pressure needed for the stripping action.

The present invention is particularly directed to a control system for a die pad for use in high speed operations which overcomes the difiiculties frequently encountered in prior systems in which a stripping action is required in high speed installations. According to the present invention a small diameter piston provides the required resistance to retraction of the die pad upon closing of the press and a larger diameter piston assists the smaller diameter piston in returning the die pad to its extended position to strip the Work from the die.

-A principal object of the invention is to provide a new and improved control system for movable die pads in presses.

Another object of the invention is to provide a hydraulic cushion for a die pad in a press having an auxiliary piston operable to assist in obtaining a stripping ac tion by the die pad.

Other and further objects of the invention will be 3,124,340 Patented Mar. 10, 1964 apparent from the following description and claims and may be understood by reference to the accompanying drawings, of which there are two sheets, which by way of illustration show preferred embodiments of the invention and what I now consider to be the best mode of applying the principles thereof. Other embodiments of the invention may be used without departing from the scope of the present invention as set forth in the appended claims.

In the drawings:

FIG. 1 is a sectional schematic view illustrating a control system for a die pad in a press constructed according to the present invention;

FIG. 2 is a sectional view through a set of dies illustrating one type of forming operation on a workpiece in which a control system like that shown in FIG. '1 may be employed; and

FIG. 3 is a sectional view of a die pad and its hydraulic cushion illustrating a modified form of the invention.

In FIIG. 1 there is illustrated a portion of a press which includes a die shoe 19 having a hydraulic cushion indicated generally at 12 mounted thereon and reacting against a movable die pad 14 which is adapted to be engaged by the Work (not shown) upon closing of the press. The hydraulic cushion comprises a housing 16 containing a cylinder block 18 which is provided at its upper end with a cylinder 20 and at its lower end with a larger diameter cylinder 22. A piston 24 is reciprocable within the cylinder 26 and has an enlarged head 26 which engages the underside of the die pad 14. A piston 28 is reciprocable within the auxiliary cylinder 22. Pins 30, which are slidable within bores 32 in the cylinder block 13, engage the head 26 on the piston 24 and the upper surface of the auxiliary piston 28 to provide a motion transmitting connection between the pistons 24 and 28.

A tank 34 contains a body of hydraulic fluid such as oil therein under a suitable low pressure such as to pounds per square inch. The oil is maintained under pressure by air under pressure supplied through a. line 36 leading to a suitable source of air under pressure. A line 38 provides a normally open fluid flow connection between the tank 34 and the lower end of the auxiliary cylinder 22. A line 49 is connected to a passage 42 in a valve indicated generally at 44 which contains a check valve 46 and a pressure relief valve 48. A passage 50 in the valve 44 provides a communication between passage 42 and a parallel passage 52 which intersects a passage 54- communicating with a line 56 which is connected to a passage 58 leading to the lower end of the hydraulic cushion cylinder 20. The passage -56) is normally closed by the check valve 46 which provides a one-way fluid connection between the tank 34 and the cylinder 20. The pressure relief valve 48 is reciprocable within a chamber 60 in the valve 44 and is urged by a spring 62 to close the communication between the passages 42 and 54. The pressure at which the valve 48 will open may be adjusted by the screw 64 so that the valve 48 opens only when a predetermined pressure is exceeded in the cylinder 20.

When the press is opened, hydraulic fluid under the pressure existing in the tank 34 flows past check valve 46 through passages 52 and 54 to line 56 and passage 58 to urge the piston 24 and the die pad 14 upwardly to an extended position relative to the die shoe it). The pistons 24 and 28 are shown in their retracted positions in FIG. 1, which condition exists at the end of the working stroke of the press. The hydraulic fluid in the cylinder 20 is forced by the piston 24 out through passage 58 to line 56 and passage 54 to the pressure relief valve 48. The pressure relief valve provides a predetermined resistance to such movement of the die pad 14 and the piston 24 and, when the pressure for which it is set is exceeded, the valve 48 will open to return the fluid through passage 42 and line 40 to the tank 34. The fluid trapped in the lower end of the cylinder 22 will be returned to the tank 34 through the line 38 as the press closes. Since the connection between the cylinder 22 and the tank 34 is normally open, the resistance to downward movement of the piston 28 is only that provided by the relatively low pressure in the tank 34 and this resistance is not appreciable as compared with that provided by the pressure relief valve 48.

When the press begins to open, the pressure relief valve 48 will close and fluid will be returned to the cylinder 20 from line 4i) past check valve 46 to tend to return the die pad 14 to its extended position. Since the diameter of the piston 24 is relatively small, the force provided by the pressure fluid reacting against the underside of the piston 24 may not be great enough to provide an eificient stripping action to strip the work from the die as the press opens. The auxiliary piston 28 being of much larger diameter than the piston 24 is constantly subjected to the pressure existing in the tank 34 and the upward force exerted by the piston 28 will be transmitted to the piston 24 through the pins 30 to assist the piston 24 in effecting the stripping operation. Thus the high pressure required upon closing of the press is provided by the small diameter piston 24 which reduces excessive movement of oil at the high pressure while the large diameter auxiliary piston 28 moves a larger quantity of oil back and forth between the cylinder 22 and tank 34 but under relatively low pressure, thereby reducing the amount of heat generated in the system due to oil movement.

FIG. 2 illustrates a set of dies provided with a hydraulic cushion embodying the principles of this invention and illustrates one type of forming operation on a workpiece in which a system of this type would be useful. The lower die shoe has mounted thereon a cylinder block indicated generally at 16 which is provided with two or more work cylinders 20 and two or more auxiliary cylinders 22. The work cylinders 20 contain pistons 24 provided with enlarged heads 26 engaging the underside of the movable die pad 14 while the auxiliary cylinders 22 contain pistons 28. The pins 30 provide a motion transmitting connection between the pistons 24 and 28. It is to be understood that a series of pins 30 may connect each piston 24 with its corresponding auxiliary piston 28. A forming punch 78 and a trimming die 72 are mounted on the lower die shoe.

The upper die shoe 74 is provided with a forming and cut-off die member 76 and a pressure plate 78 which is urged to an extended position by springs 80. A reciprocating die member 82 is also urged to an extended position by a spring 84.

The workpiece 86 is adapted to rest upon the upper surfaces of the die members 70 and 72 and the die pad 14 when the press is open. The pistons 24 and 28 are in their upper extended positions at this time due to the pressure fluid supplied thereto through the fluid connections illustrated in FIG. 1. As the press descends, the reciprocable die members 78 and 82 engage the work to clamp the work against the lower die members 70 and 72. As the ram descends further, the upper die member 76 engages the work to perform the cut-oif operation and to form the work to the desired shape, thus forcing the die pad 14 to its retracted position against the resistance oflered by the fluid trapped in the cylinders 20 which escapes past the pressure relief valve 48 as described. When the press opens, the larger diameter pistons 28 which are always subjected to the pressure in the tank 34 will assist the small diameter pistons 24 to return the die pad 14 to its extended position to strip the workpiece 86 from the punch 70. The stripping arrangement disclosed will obviously be useful in other forming operations on a workpiece.

FIG. 3 illustrates a modified form of the invention in which the cylinder block 112 is provided with a large diameter auxiliary cylinder 114- and a smaller diameter work cylinder 116. The work piston 118 and the auxiliary piston are combined in this form of the invention into a single piston element having different diameters at its opposite ends. The auxiliary piston engages the die pad 14. The auxiliary cylinder 114 is connected to the tank 34 through the line 38 which is a normally open fluid connection, while the work cylinder 116 is connected to the tank 34 by the line 56 which leads to the valve 44 illustrated in FIG. 1. As in the previous modification, both the auxiliary piston 120 and the work piston 118 are effective to supply the stripping pressure upon opening of the press, while the high resistance to movement of the die pad upon closing of the press is provided only by the small diameter piston 118.

While I have illustrated and described preferred cmbodiments of my invention, it is understood that these are capable of modification, and I therefore do not wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. In a ram type press having a movable die pad engaged by the work so as to be moved to a retracted position upon closing of the press and a hydraulic cushion for said pad to resist such movement of said pad and to effect return movement of said pad upon opening of the press, said hydraulic cushion comprising a hydraulic work cylinder on said press having a piston reciprocable therein, a tank containing hydraulic fluid under relatively low pressure, a hydraulic fluid connection between said tank and said cylinder through which fluid is supplied under said tank pressure to said cylinder to move said work piston to its extended position, a check valve in said connection preventing return fiow therethrough, a return line through which hydraulic fluid is returned from said cylinder to said tank, a normally closed pressure relief valve in said return line which opens to provide predetermined resistance substantially greater than tank pressure to movement of said piston to its retracted position upon closing of the press, an auxiliary hydraulic cylinder on said press of larger diameter than said hydraulic cushion cylinder, a piston reciprocable in said auxiliary cylinder, an open hydraulic fluid connection between said tank and said auxiliary cylinder whereby hydraulic fluid under tank pressure is supplied to said auxiliary cylinder and reacts on said piston therein, one of said cylinders and the piston therein reacting on said die pad so as to resist retraction thereof upon closing of the press with a resistance substantially greater than tank pressure, and a positive motion transmitting connection between said pistons, both of said cylinders and the pistons therein being arranged with respect to said die pad so that movement of both of said pistons to their extended positions under pressure of the hydraulic fluid in said tank is transmitted to said die pad to move the latter to its extended position to strip the work from the die upon opening of the press.

2. In a ram type press having a movable die engaged by the Work and moved to a retracted position upon closing of the press and a hydraulic cushion for said die to resist such movement and to effect return movement of said die upon opening of the press, said hydraulic cushion comprising a pair of hydraulic cylinders on the press, each having a piston reciprocable therein, one of said cylinders and the piston therein reacting against said die so as to resist retraction thereof upon closing of the press, one of said pistons being of substantially smaller diameter than the other of said pistons, a positive motion transmitting connection between said pistons, a tank containing hydraulic fluid under relatively low pressure, a hydraulic fluid connection between said tank and each of said cylinders through which hydraulic fluid is continuously supplied under tank pressure to said cylinders to bias said pistons toward said die, both of said cylinders and the pistons therein being arranged with respect to said die so that said pistons bias said die to its extended position, a check valve in the connection to the smaller diameter cylinder preventing return flow therethrough, a hydraulic return line through which hydraulic fluid is returned from said smaller diameter cylinder to said tank, and a normally closed pressure relief valve in said return line which opens to provide predetermined resistance substantially greater than tank pressure to movement of said die upon closing of the press, said cylinders being disposed relative to each other so that one of said cylinders and the piston therein is between the other of said cylinders and said die, said hydraulic fluid connection affording unrestricted fluid flow from the larger diameter cylinder to said tank.

3. In a press having a movable die pad engaged by the work so as to be moved to a retracted position upon closing of the press and a hydraulic cushion for said pad to resist such movement of said pad and to effect return movement of said pad upon opening of the press, said hydraulic cushion comprising a hydraulic cylinder on said press having a piston reciprocable therein and reacting against said pad so as to resist retraction thereof upon closing of the press, a tank containing hydraulic fluid under relatively low pressure, a hydraulic fluid connection between said tank and said cylinder through which hydraulic fluid is supplied under tank pressure to said cylinder to urge the piston therein in one direction, a check valve in said connection preventing return flow therethrough, a hydraulic return line through which hydraulic fluid is returned from said cylinder to said tank, a normally closed pressure relief valve in said return line which opens to provide predetermined resistance substantially greater than tank pressure to movement of said die pad to its retracted position upon closing of the press, an auxiliary hydraulic cylinder on said press of larger diameter than said hydraulic cushion cylinder, a piston reciprocable in said auxiliary cylinder, a positive motion transmitting connection between said piston in said larger diameter cylinder and said die pad, and an open hydraulic fluid connection between said tank and said auxiliary cylinder through which hydraulic fluid under tank pressure is supplied to said auxiliary cylinder, both of said cylinders and the pistons therein being arranged with respect to said die pad so that such pistons under the influence of tank pressure bias said pad to its extended position to strip the work from the die upon opening of the press.

4. In a ram type press having a movable die pad engaged by the work so as to be moved to a retracted position upon closing of the press and a hydraulic cushion for said pad to resist such movement of said pad and to effect return movement of said pad upon opening of the press, said hydraulic cushion comprising a hydraulic cylinder on said press having a piston reciprocable therein and reacting against said pad so as to resist retraction thereof upon closing of the press, a tank containing hydraulic fluid under relatively low pressure, a hydraulic fluid connection between said tank and said cylinder through which hydraulic fluid is supplied under tank pressure to said cylinder to move said pad to its extended position, a check valve in said connection preventing return flow therethrough, a hydraulic return line through which hydraulic fluid is returned from said cylinder to said tank, a normally closed pressure relief valve in said return line which opens to provide predetermined resistance substantially greater than tank pressure to movement of said die pad to its retracted position upon closing of the press, an auxiliary hydraulic cylinder on said press of larger diameter than said hydraulic cushion cylinder, a piston reciprocable in said auxiliary cylinder, an open hydraulic fluid connection between said tank and said auxiliary cylinder through which hydraulic fluid under tank pressure is supplied to said auxiliary cylinder, and a positive motion transmitting connection between said auxiliary piston and said die pad, both of said cylinders and the pistons therein being arranged with respect to said die pad so that movement of both of said pistons under pressure of the hydraulic fluid in said tank is transmitted to said die pad to strip the work from the die upon opening of the press.

5. In a, ram type press having a movable die pad engaged by the work so as to be moved to a retracted position upon closing of the press and a hydraulic cushion for said pad to resist such movement of said pad and to effect return movement of said pad upon opening of the press, said hydraulic cushion comprising a hydraulic work cylinder on said press having a piston reciprocable therein and reacting against said pad so as to resist retraction thereof upon closing of the press, a tank containing hydraulic fluid under relatively low pressure, a hydraulic fluid connection between said tank and said cylinder through which hydraulic fluid is supplied under tank pressure to said cylinder to move said pad to its extended position, a check valve in said connection preventing return flow therethrough, a hydraulic return line through which hydraulic fluid is returned from said hydraulic cylinder to said tank, a normally closed pressure relief valve in said return line which opens to provide predetermined resistance substantially greater than tank pressure to movement of said die pad to its retracted position upon closing of the press, an auxiliary hydraulic cylinder on said press of larger diameter than said hydraulic cushion cylinder, a piston reciprocable in said auxiliary cylinder, an open hydraulic fluid connection between said tank and said auxiliary cylinder through which hydraulic fluid under tank pressure is supplied to said auxiliary cylinder, and a positive motion transmitting connection between said pistons, both of said cylinders and the pistons therein being arranged with respect to said die pad so that such pistons under the influence of tank pressure bias said pad to its extended position to strip the work from the die upon opening of the press.

6. In a ram type press having a movable die pad engaged by the work so as to be moved to a retracted position upon closing of the press and a hydraulic cushion for said pad to resist such movement of said pad and to effect return movement of said pad upon opening of the press, said hydraulic cushion comprising a hydraulic cylinder on said press having a piston reciprocable therein and reacting on said die pad to resist retraction thereof, a tank containing hydraulic fluid under relatively low pressure, a hydraulic fluid connection between said tank and said cylinder through which hydraulic fluid is supplied to said cylinder under tank pressure to move said piston to its extended position, a check valve in said connection preventing return flow therethrough, a hydraulic return line through which hydraulic fluid is returned from said cylinder to said tank, a normally closed pressure relief valve in said return line which opens to provide predetermined resistance substantially greater than tank pressure to movement of said piston to its retracted position upon closing of the press, an auxiliary hydraulic cylinder on said press of larger diameter than said hydraulic cushion cylinder, a piston reciprocable in said auxiliary cylinder and reacting against said die pad, an open hydraulic fluid connection between said tank and said auxiliary cylinder through which hydraulic fluid under tank pressure is supplied to said auxiliary cylinder, and a positive motion transmitting connection between said pistons, both of said cylinders and the pistons therein being arranged with respect to said die pad so that '7 8 movement of both of said pistons to their extended posi- 1,772,914 Rode Aug. 12, 1930 tions under pressure of the hydraulic fiuid in said tank is 1,778,229 Rode Oct. 14, 1930 transmitted to said die pad to move the latter to its ex- 1,849,690 Rode Mar. 15, 1932 tended position to strip the work from the die upon 2,300,162 Maude Oct. 27, 1942 opening of the press. 5 2,842,357 Williamson July 8, 1958 References Cited in the file of this patent 2333307 Wllhamson 1960 UNITED STATES PATENTS FOREIGN PATENTS 1,706,074 Rode Mar. 19, 192 616,266 Germany July 24, 1935 

1. IN A RAM TYPE PRESS HAVING A MOVABLE DIE PAD ENGAGED BY THE WORK SO AS TO BE MOVED TO A RETRACTED POSITION UPON CLOSING OF THE PRESS AND A HYDRAULIC CUSHION FOR SAID PAD TO RESIST SUCH MOVEMENT OF SAID PAD AND TO EFFECT RETURN MOVEMENT OF SAID PAD UPON OPENING OF THE PRESS, SAID HYDRAULIC CUSHION COMPRISING A HYDRAULIC WORK CYLINDER ON SAID PRESS HAVING A PISTON RECIPROCABLE THEREIN, A TANK CONTAINING HYDRAULIC FLUID UNDER RELATIVELY LOW PRESSURE, A HYDRAULIC FLUID CONNECTION BETWEEN SAID TANK AND SAID CYLINDER THROUGH WHICH FLUID IS SUPPLIED UNDER SAID TANK PRESSURE TO SAID CYLINDER TO MOVE SAID WORK PISTON TO ITS EXTENDED POSITION, A CHECK VALVE IN SAID CONNECTION PREVENTING RETURN FLOW THERETHROUGH, A RETURN LINE THROUGH WHICH HYDRAULIC FLUID IS RETURNED FROM SAID CYLINDER TO SAID TANK, A NORMALLY CLOSED PRESSURE RELIEF VALVE IN SAID RETURN LINE WHICH OPENS TO PROVIDE PREDETERMINED RESISTANCE SUBSTANTIALLY GREATER THAN TANK PRESSURE TO MOVEMENT OF SAID PISTON TO ITS RETRACTED POSITION UPON CLOSING OF THE PRESS, AN AUXILIARY HYDRAULIC CYLINDER ON SAID PRESS OF LARGER DIAMETER THAN SAID HYDRAULIC CUSHION CYLINDER, A PISTON RECIPROCABLE IN SAID AUXILIARY CYLINDER, AN OPEN HYDRAULIC FLUID CONNECTION BETWEEN SAID TANK AND SAID AUXILIARY CYLINDER WHEREBY HYDRAULIC FLUID UNDER TANK PRESSURE IS SUPPLIED TO SAID AUXILIARY CYLINDER AND REACTS ON SAID PISTON THEREIN, ONE OF SAID CYLINDERS AND THE PISTON THEREIN REACTING ON SAID DIE PAD SO AS TO RESIST RETRACTION THEREOF UPON CLOSING OF THE PRESS WITH A RESISTANCE SUBSTANTIALLY GREATER THAN TANK PRESSURE, AND A POSITIVE MOTION TRANSMITTING CONNECTION BETWEEN SAID PISTONS, BOTH OF SAID CYLINDERS AND THE PISTONS THEREIN BEING ARRANGED WITH RESPECT TO SAID DIE PAD SO THAT MOVEMENT OF BOTH OF SAID PISTONS TO THEIR EXTENDED POSITIONS UNDER PRESSURE OF THE HYDRAULIC FLUID IN SAID TANK IS TRANSMITTED TO SAID DIE PAD TO MOVE THE LATTER TO ITS EXTENDED POSITION TO STRIP THE WORK FROM THE DIE UPON OPENING OF THE PRESS. 